#include "apue.h"
#include <errno.h>
#include <limits.h>

#ifdef PATH_MAX
static long pathmax = PATH_MAX;
#else
static long pathmax = 0;
#endif

static long posix_version = 0;
static long xsi_version = 0;

/* If PATH_MAX is indeterminate, no guarantee this is adequate */
#define PATH_MAX_GUESS 1024

char *
path_alloc(size_t *sizep) /* also return allocated size, if nonnull */
{
	char	*ptr;
	size_t	size;

	if (posix_version == 0) {
		posix_version = sysconf(_SC_VERSION);
	}

	if (xsi_version == 0) {
		xsi_version = sysconf(_SC_XOPEN_VERSION);
	}

	if (pathmax == 0) {		/* first time through */
		errno = 0;
		/*
			The value returned by pathconf is the maximum size of a relative pathname 
			when the first argument is the working directory, 
			so we specify the root as the first argument and add 1 to the result. 
			If pathconf indicates that PATH_MAX is indeterminate, 
			we have to punt and just guess a value.
		*/
		if ((pathmax = pathconf("/", _PC_PATH_MAX)) < 0) {
			if (errno == 0) {
				/* it's indeterminate */
				pathmax = PATH_MAX_GUESS;
			} else {
				err_sys("pathconf error for _PC_PATH_MAX");
			}
		} else {
			/* add one since it's relative to root */
			pathmax++;
		}
	}

	/*
	   Before POSIX.1-2001, we aren't guaranteed that PATH_MAX includes
	   the terminating null byte. Same goes for XPG3.
	*/
	if ((posix_version < 200112L) && (xsi_version < 4)) {
		size = pathmax + 1;
	} else {
		size = pathmax;
	}

	if ((ptr = malloc(size)) == NULL) {
		err_sys("malloc error for pathname");
	}

	if (sizep != NULL) {
		*sizep = size;
	}

	return (ptr);
}
		
